Neutral Silicon-Vacancy Center in Diamond: Spin Polarization and Lifetimes.

We demonstrate optical spin polarization of the neutrally charged silicon-vacancy defect in diamond (SiV0), an S = 1 defect which emits with a zero-phonon line at 946 nm. The spin polarization is found to be most efficient under resonant excitation, but nonzero at below-resonant energies. We measure an ensemble spin coherence time T-2 > 100 mu s at low-temperature, and a spin relaxation limit of T-1 > 25 s. Optical spin-state initialization around 946 nm allows independent initialization of SiV0 and NV- within the same optically addressed volume, and SiV0 emits within the telecoms down-conversion band to 1550 nm: when combined with its high Debye-Waller factor, our initial results suggest that SiV0 is a promising candidate for a long-range quantum communication technology.